1. Field of the Invention
This invention relates to a structure of an engine unit for a vehicle including an engine and a power train.
2. Description of the Prior Art
It has been known to mount an engine body sideways on a vehicle body so that the crankshaft extends in the transverse direction of the vehicle body and to mount a transmission and a differential in parallel to the crankshaft. (See, for instance, Japanese Unexamined Patent Publication No. 1(1989)-31655 and U.S. Pat. No. 4,915,070).
In an automotive engine, auxiliary mechanisms which are relatively small in size and give relatively light load to the engine such as an oil pump for lubricating the engine and a water pump are generally disposed on the front end of the engine and connected to the crankshaft directly or by way of gears, while those which give relatively heavy load to the engine such as a pump for a power steering and an alternator are generally disposed on a side of the engine near the front or rear end of the engine and driven by the crankshaft by way of a belt or chain. For example, an engine disclosed in West German Patent No. 3838073 is mounted sideways on the vehicle body with a transmission disposed in parallel to the engine and is slanted rearward, and auxiliary mechanisms are disposed in a space produced by the rearward slant of the engine and are driven by the crankshaft by way of a belt.
By the way, also in a front-engine front-drive vehicle where the engine is mounted sideways, the transmission is generally mounted in series with the engine body, and accordingly, an oil pan is required for each of the engine body and the transmission (the power train), which complicates the structure of the engine unit and increases the amount of oil required. This problem cannot be overcome even with the structure disclosed in Japanese Unexamined Patent Publication No. 1(1989)-316559 where the transmission is disposed in parallel to the crankshaft of the engine in order to reduce the sum of the lengths of the crankshaft and the transmission in the transverse direction of the vehicle body.
That is, oil should be stored in the oil pan in an amount sufficient to prevent the oil level from falling below the oil strainer when the vehicle makes a sudden start, sudden stop or sharp turn, and accordingly, a large amount of oil must be stored in both the oil pans for the engine and the transmission. When the oil pan is formed by deep draw or a baffle plate is provided in the bottom of the oil pan, production of the oil pan is complicated and production cost is increased.
There has been a demand for mounting auxiliary mechanisms in a space on the front side or the rear side of the oil pan which is a relatively dead space. However an attempt to dispose the auxiliary mechanism in such a space involves a problem that the part for mounting the auxiliary mechanism must be reinforced in order to ensure bearing rigidity for belt tension and a space for passing the auxiliary mechanism driving shaft which is connected to the crankshaft must be provided, which results in reduction of the volume of the oil pan and failure in ensuring the amount of oil. Thus the conventional arts have failed in sufficiently utilizing the dead spaces on the front and rear side of the oil pan in disposing the auxiliary mechanisms.
Further the engine body is sometimes slanted in one direction relative to the vertical plane passing through the crankshaft of the engine in view of layout in the engine room. In such a case, the center of gravity of the engine body can be off-centered or shifted upward, which can be enhanced depending on the arrangement of the auxiliary mechanisms to cause rolling of the vehicle body.
Further when the power train is disposed behind the engine, the transmission cannot be sufficiently cooled by airflow during running and an external oil cooler for cooling the transmission oil comes to be necessary, which is undesirable in view of space, cost and weight.